The present invention relates to a metal laminate type cylinder head gasket having grommets with different thicknesses to prevent upward expansion or curve of a cylinder head of an engine.
In order to provide high power and light weight for an automobile engine, the engine or at least a cylinder head is made of an aluminum alloy. Since the aluminum alloy does not have high rigidity, when a gasket is installed in the engine, sealing problem between the cylinder head and the cylinder block may occur.
Namely, in case a plurality of cylinder bores is arranged in one or a longitudinal direction, when the gasket is tightened between the cylinder head and the cylinder block by bolts, sealing means situated around the respective cylinder bores are compressed. In this respect, the bolts located in a middle portion of the engine operate to tighten two, i.e. right and left, portions of the sealing means relative to the bolt, while the bolts at the longitudinal ends of the engine only tighten one portion of the sealing means. Thus, the bolts at the longitudinal ends operate to tighten the sealing means at a pressure generally twice as much as the pressure for the rest of the portion of the sealing means.
The unbalanced tightening pressure causes the middle portion of the cylinder head to move upwardly. As a result, the equal sealing pressure is not applied to the sealing means. In a long usage, leaking occurs in the cylinder head or other holes.
In order to support the edges of the cylinder head, beads may be formed. In U.S. Pat. No. 4,834,399, a bead is formed around the entire outer portion of the gasket. However, since the bead completely surrounds the edge portion of the gasket, the bead can not support required portions.
In Japanese Utility Model Publication (KOKAI) No. 61-69450, longitudinal end portions of a gasket are made thicker than a middle portion of the gasket. The thickness of the gasket is adjusted such that the height of beads around the cylinder bores located at the longitudinal end portions is made higher than that around the cylinder bore in the middle portion of the gasket, or that small holes, such as water holes, oil holes and so on, located at the longitudinal end portions are equipped with sealing beads, while a bead is not formed around the small holes at the middle portion.
In the above case, if the beads are compressed for a long time in a high temperature condition, the beads may creep and loose the spring ability. Therefore, the sealing ability decreases in the above case. Also, some of the holes do not have sealing beads to cause a sealing problem.
In Japanese Utility Model Publication (KOKOKU) No. 4-47405, a gasket includes a plate having beads, and a thick plate laminated on the plate, wherein longitudinal ends of the thick plate are folded to form thick portions at the longitudinal ends.
Further, in some cases, the longitudinal ends of a gasket are made thick by beads or extra plates.
Accordingly, one object of the invention is to provide a metal laminate gasket, which can substantially prevent deformation of a cylinder head caused by unbalanced surface pressure on the sealing means.
Another object of the invention is to provide a metal laminate gasket as stated above, wherein all the holes can be securely sealed.
A further object of the invention is to provide a metal laminate gasket as stated above, wherein creep relaxation of the beads used for sealing around the holes can be prevented.
A still further object of the invention is to provide a metal laminate gasket as stated above, which can be easily and economically manufactured.
Further objects and advantages of the invention will be apparent from the following description of the invention.